Precise measurements of the cosmic ray proton energy spectrum in the “knee” region
Z. Cao, F. Aharonian, Y.X Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, Wei‐Hao Bian, A.V Bukevich, Chang Cai, Weiling Cao, Zhe Cao, Jin Chang, J. F. Chang, A.M. Chen, E. S. Chen, Guohua Chen, Hongyu Chen, Liang Chen, Long Chen, M. J. Chen, M.L. Chen, Qin Chen, S. Chen, Chen Sh, S. Z. Chen, T. L. Chen, X.B. Chen, X.J. Chen, Y. Chen, Na Cheng, Yaodong Cheng, M. C. Chu, Maxwell Cui, S. W. Cui, Xiaohong Cui, Y. D. Cui, B. Z. Dai, H.L. Dai, Zi-Gao Dai, Danzengluobu, Yu-xiang Diao, X.Q Dong, K. K. Duan, J. H. Fan, Yi-Zhong Fan, Jun Fang, J. Fang, K. Fang, C. Feng, Hansheng Feng, Lei Feng, S.H. Feng, X.T Feng, Yuliang Feng, Y. L. Feng, S. Gabici, Bo Gao, C. D. Gao, Qing Gao, Wei Gao, Wei Gao, M.M Ge, Tingting Ge, Li‐Sheng Geng, Gwenael Giacinti, G. Gong, Q. B. Gou, M. H. Gu, Fulai Guo, Jian Guo, X. L. Guo, Yanjun Guo, Yao Guo, Y. A. Han, O. A. Hannuksela, M. Zahid Hasan, H.H He, Hongbin He, Jiangbiao He, Xiaoyang He, Yuefeng He, S. Hernández-Cadena, Biao Hou, Chang Hou, Xiaoyu Hou, H. B. Hu, S. C. Hu, Chen Huang, D.H Huang, J. Huang, T.Q Huang, Weidong Huang, X. T. Huang, X.Y Huang, Y. Huang, Yanyi Huang, Xiangdong Ji, H.Y Jia, K. Jia
Abstract
We report the high-purity identification of cosmic-ray (CR) protons and a precise measurement of their energy spectrum from 0.15 to 12 PeV using the Large High Altitude Air Shower Observatory (LHAASO). Abundant event statistics, combined with the simultaneous detection of electrons/photons, muons, and Cherenkov light in air showers, enable spectroscopic measurements with statistical and systematic precision comparable to satellite data at lower energies. The proton spectrum shows significant hardening relative to low-energy extrapolations, culminating at 3 PeV, followed by sharp softening. This distinct spectral structure closely aligned with the knee in the all-particle spectrum points to the emergence of a new CR component at PeV energies that might be linked to the dozens of PeVatrons recently discovered by LHAASO, and offers crucial clues to the origin of Galactic cosmic rays.